This invention relates generally to analytical testing of chemical and physical properties and their changes within an area under test (AUT). In particular, the invention relates to systems and methods for measuring and monitoring concentrations of radioactive gases such as radon, thoron and other materials within a gaseous environment of the AUT in-situ by spectroscopic and/or electrostatic means.
There are numerous devices presently available for detecting the presence of radioactive gas (e.g., radon) within an environment. Such devices, for example, are illustrated in U.S. Pat. No. 4,992,658, issued Feb. 12, 1991 (the ""658 patent) and U.S. Pat. No. 5,107,108, issued Apr. 21, 1992 (the ""108 patent), both to Ramsey et al. The disclosure of these U.S. patents are incorporated by reference herein in their entireties. The radon monitoring device disclosed in the ""658 patent includes a housing having an electret ion chamber. A technician locates the device in an environment to be monitored and opens a cover of the housing to permit radon in the environment to enter the electret ion chamber by diffusion. As the radon decays, radiation emitted by the decay process of the radon gas generates ions in the air inside of the electret ion chamber. The electret, having been pre-charged with a positive polarity, attracts the electrons (negative ions) to its surface. Every ion that is collected by the electret surface results in a reduction of charge in the electret. Measurements of a surface voltage, an indication of charge, of the electret before and after exposure to radon may be utilized to determine the concentration of radon encountered during exposure. For example, exposure to a predetermined concentration of radon over a predetermined period of time is known to result in the electret discharging by a defined amount of voltage. By recording a period of time of an actual exposure and the resulting discharge of voltage (e.g., surface voltage measured prior to exposure minus surface voltage measured after the exposure), an average concentration of radon within an environment of interest may be determined. The above described calculation assumes accurate knowledge of the initial electret charge and an ideal electret having no leakage or other loss of charge due to factors other than from exposure to radon.
Another device referred to as a continuous radon detector is described in U.S. Pat. No. 4,871,914, issued Oct. 3, 1989, to William E. Simon et al. (the ""914 Patent). The ""914 Patent describes an electronic detector that uses a diffused-junction photodiode sensor to measure alpha particles. The device reports radon gas levels electronically after a given period of time (e.g., a total count of alpha particles). Other conventional electronic radiation detector devices include a thallium activated cesium iodide scintillation crystal coated over a silicon pin diode or photodiode. Another conventional detector consists of a silver activated zinc sulfide scintillation crystal coated over a silicon pin diode.
A perceived disadvantage of these devices is that they typically require physical human intervention during the test period. The inventors have realized that the perceived disadvantage may be remedied by employing telemetry and/or cellular communication for transmitting data in virtual time mode. As such, physical human intervention can be avoided.
The inventors have further realized a number of deficiencies in the current testing procedures and devices. In conventional systems, a technician typically visits a test site and operates the measuring device more than once so that actual measurements for determining a concentration of radon in the test site can be taken. For example, a technician initiates a test by physically setting the device in an area of the test site and exposes the measuring device (e.g., the detector or absorbing surface of the device) to the test area (e.g., atmosphere within the area of the test site). To complete the test, the technician returns to the test site and retrieves the measuring device so that the measurement and calculation can be performed. For some units, the technician performs the measurement calculation at the test site. In other units, the technician carefully tranports the measuring device to a testing facility where the measurement and calculations are made.
When testing procedures include the utilization of a device having a charcoal canister collector, a qualified technician completes the testing by completely sealing the canister and returns the canister to a test facility. At the test facility a gamma counter is use to measure an amount of gamma radiation emitted from a Pb-214 isotope generated by the adsorbed radon gas. When testing procedures include the use of a continuous monitoring device such as alpha or gamma sensors, a qualified individual completes the test by returning to the test site so that the sensor can be read and the measurements interpreted. When the measuring device includes an electret, leakage due to cleanliness of a housing enclosing the electret, humidity and other factors related to multiple handling of the device affects the xe2x80x9cas measuredxe2x80x9d parameters. Referring again to the charcoal canister device, trapped radioactive constituents are time dependent, as such the accuracy of the xe2x80x9cas measuredxe2x80x9d value is a function of the amount of time required to return the canister to a certified laboratory for measurement. Furthermore, the radioactive decay of radon and its progeny further increase the error of accuracy when there is a delay in performing measurement calculations. In recognition of the possibility of such inaccuracies the Environmental Protection Agency (EPA) has published correction factors to account for different time periods between collection and measurement (e.g., delayed measurement calculation). An example of such an EPA publication is EPA 520/5-87-005, June, 1987, EERF Standard Operating Procedures for Radon-222 Measurement Using Charcoal Canisters, D. J. Gray, S. T. Windham, March, 1987.
It should be appreciated that human intervention in monitoring procedures, whether an intended or unintended (e.g., tampering with the device) step of the procedures, have been known to introduce errors in the obtained results. Therefore, it is preferable to minimize such intervention by limiting the number of times that a technician returns to the test site. Additionally, it should be appreciated that it is often cumbersome, inconvenient and/or inefficient for personnel (e.g., the technician) to go back to the testing site in order to perform final readings and/or retrieve a monitoring device for measurement at the test facility. Also, not every attempt to test an environment of interest is initially successful. A number of factors including, for example, failure of the monitoring device itself, misuse or tampering by non-certified persons at the test site may result in the need for another test. Such misuse or tampering can be, for example, an intentional or unintentional interruption resulting from a non-technician altering one or more parameters of the test procedures. As a result, a qualified technician would be required to revisit the test site, install a new device (or correct parameters of the current device) and initiate another test cycle.
In view of the foregoing, the inventors have realized that a need exists for a monitoring system that performs site specific collecting, detecting and measuring operations, substantially independent of conditions not directly related to the radioactive gas and suspended aerosols present at the test site, and that is capable of transmitting continuous or discrete results of measuring operations to a remote facility for real-time analysis. Additionally, the inventors have realized that it would be advantageous to employ a device that is responsive to control signals transmitted from, for example, the remote monitoring facility. The control signals may alter one or more parameters during, for example, a pre-test phase of the detecting and measuring operations, to improve the accuracy of the test results.
Accordingly, the present invention provides improved methods and apparatus for collecting, detecting and measuring radioactive gases (e.g., radon) and suspended aerosols within an environment of interest that addresses the above described and other perceived deficiencies in conventional monitoring devices.
It is an object and advantage of this invention to provide an improved system for collecting, detecting and measuring radioactive gases (e.g., radon) and suspended aerosols within an environment of interest.
It is another object and advantage of this invention to provide an analytical testing method having the ability to remotely measure and monitor chemical and physical properties and their changes within an environment of interest.
It is another object and advantage of this invention to provide a programmable monitoring device that includes a sensor for collecting ions generated by a decay of a radioactive gas, a detector for selectively measuring a change in an electrostatic potential of the sensor due to the collected ions, a microprocessor and a transmitter for transmitting the measured changes to a data processing system for real-time and/or virtual real-time analysis of the changes to determine a concentration of the radioactive gas or suspended aerosols within an environment of interest.
It is yet another object and advantage of this invention to provide a programable monitoring device that includes a sensor for collecting ions generated by a decay of a radioactive gas, a detector for selectively measuring radioactive particles or electromagnetic radiation of a given energy, a microprocessor and a transmitter for transmitting the measured changes to a data processing system for real-time and/or virtual real-time analysis of the changes to determine a concentration of the radioactive gas or suspended aerosols within an environment of interest.
It is still another object and advantage of this invention to provide a programmable monitoring device having the aforementioned sensor, detectors, microprocessor and transmitter, and that also includes a receiver for receiving signals from the data processing system. The signals including parameters for adjusting the selective measuring process employed by the detector in response to, for example, preferred values of a frequency of measuring and a duration of testing that corresponding to the determined concentration of the radioactive gas.
It is another object and advantage of the invention to provide a remotely programmable device for real-time detection and measurement of a concentration of radioactive gas such as radon, thoron and other materials in-situ by spectroscopic and/or electrostatic means and which saves the lives of personnel by relaying virtually instantaneous information to appropriate personnel such that the proper action is taken long before complications develop.
Further objects and advantages of this invention will become more apparent from a consideration of the drawings and ensuing description.
The foregoing objects are realized by methods and apparatus in accordance with embodiments of this invention, wherein a system is presented for detecting and measuring a concentration of radioactive gas and suspended aerosol within an environment of interest. The system includes a testing facility having a data processing system and a monitoring device located within the environment of interest. The monitoring device is operatively coupled to the data processing system. For example, the monitoring system includes a radiotelephone or the like for accessing the data processing system via a conventional telecommunication system.
The monitoring device includes a detector having a housing that defines a chamber, a collector that is located within the chamber and a sensor electrically coupled to the collector. The housing includes at least one opening for allowing radioactive gas and suspended aerosol within the environment of interest to enter the chamber. The collector collects ions generated by a decay of radioactive gas and suspended aerosol within the chamber.
In one embodiment, the sensor selectively measures changes in an electrostatic potential of the collector in response to an accumulation of the generated ions. In another embodiment, the sensor includes a material disposed within either an electric or a magnetic field formed within the sensor. The material has optical properties that vary in response to changes in the formed field. Changes over time of the optical properties is representative of changing field strengths.
The monitoring device also includes a transmitter for transmitting, in one embodiment, the measured changes in the electrostatic potential to the data processing system. In another embodiment, the transmitter transmits the changing field strength to the data processing system. The data processing system includes application programming logic for determining the concentration of radioactive gas and suspended aerosol within the environment of interest from either of the measured changes in the electrostatic potential or the changing field strength.